.\" $OpenBSD: pthreads.3,v 1.41 2013/07/16 15:21:11 schwarze Exp $
.\" David Leonard <d@openbsd.org>, 1998. Public domain.
.Dd $Mdocdate: July 16 2013 $
.Dt PTHREADS 3
.Os
.Sh NAME
.Nm pthreads
.Nd POSIX 1003.1c thread interface
.Sh DESCRIPTION
A thread is a flow of control within a process.
Each thread represents a minimal amount of state:
normally just the CPU state and a signal mask.
All other process state (such as memory, file descriptors)
is shared among all of the threads in the process.
.Pp
In
.Ox ,
threads use a 1-to-1 implementation,
where every thread is independently scheduled by the kernel.
.Pp
For the purpose of this document,
the functions available are grouped in the following categories.
For further information, see the individual man page for each function.
.Pp
.Bl -dash -offset indent -compact
.It
Attribute Object Routines
.It
Barrier Routines
.It
Cleanup Routines
.It
Condition Variable Routines
.It
Mutex Routines
.It
Non Portable Extensions
.It
Per-Thread Context Routines
.It
Read/Write Lock Routines
.It
Spinlock Routines
.It
Thread Routines
.El
.Ss Attribute Object Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_attr_getdetachstate()" -compact
.It Fn pthread_attr_init
Initialise a threads attribute object.
.It Fn pthread_attr_destroy
Destroy a threads attribute object.
.It Fn pthread_attr_getdetachstate
Get detachstate attribute.
.It Fn pthread_attr_setdetachstate
Set detachstate attribute.
.It Fn pthread_attr_getstack
Get stackaddr and stacksize attributes.
.It Fn pthread_attr_setstack
Set stackaddr and stacksize attributes.
.It Fn pthread_attr_getstackaddr
Get stackaddr attribute.
.It Fn pthread_attr_setstackaddr
Set stackaddr attribute.
.It Fn pthread_attr_getstacksize
Get stacksize attribute.
.It Fn pthread_attr_setstacksize
Set stacksize attribute.
.It Fn pthread_attr_getguardsize
Get guardsize attribute.
.It Fn pthread_attr_setguardsize
Set guardsize attribute.
.El
.Ss Barrier Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_barrierattr_getpshared()" -compact
.It Fn pthread_barrier_init
Initialize a barrier object.
.It Fn pthread_barrier_destroy
Destroy a barrier object.
.It Fn pthread_barrier_wait
Synchronize at a barrier.
.It Fn pthread_barrierattr_init
Initialize a barrier's attribute object.
.It Fn pthread_barrierattr_destroy
Destroy a barrier's attribute object.
.It Fn pthread_barrierattr_getpshared
Get the process-shared attribute of the barrier attribute's object.
.It Fn pthread_barrierattr_setpshared
Set the process-shared attribute of the barrier attribute's object.
.El
.Ss Cleanup Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_cleanup_push()" -compact
.It Fn pthread_atfork
Register fork handlers.
.It Fn pthread_cleanup_pop
Call the first cleanup routine.
.It Fn pthread_cleanup_push
Add a cleanup function for thread exit.
.El
.Ss Condition Variable Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_condattr_setclock()" -compact
.It Fn pthread_cond_init
Create a condition variable.
.It Fn pthread_cond_destroy
Destroy a condition variable.
.It Fn pthread_cond_broadcast
Unblock all threads waiting for a condition variable.
.It Fn pthread_cond_signal
Unblock a thread waiting for a condition variable.
.It Fn pthread_cond_timedwait
Wait on a condition variable until a specific point in time.
.It Fn pthread_cond_wait
Wait on a condition variable.
.It Fn pthread_condattr_init
Initialise a condition variable attribute object.
.It Fn pthread_condattr_destroy
Destroy a condition variable attribute object.
.It Fn pthread_condattr_getclock
Get clock attribute.
.It Fn pthread_condattr_setclock
Set clock attribute.
.El
.Ss Mutex Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_mutexattr_getprioceiling()" -compact
.It Fn pthread_mutex_init
Create a mutex.
.It Fn pthread_mutex_destroy
Free resources allocated for a mutex.
.It Fn pthread_mutex_lock
Lock a mutex.
.It Fn pthread_mutex_timedlock
Attempt to lock a mutex before a specific point in time.
.It Fn pthread_mutex_trylock
Attempt to lock a mutex without blocking.
.It Fn pthread_mutex_unlock
Unlock a mutex.
.It Fn pthread_mutexattr_init
Mutex attribute operations.
.It Fn pthread_mutexattr_destroy
Mutex attribute operations.
.It Fn pthread_mutexattr_getprioceiling
Mutex attribute operations.
.It Fn pthread_mutexattr_setprioceiling
Mutex attribute operations.
.It Fn pthread_mutexattr_getprotocol
Mutex attribute operations.
.It Fn pthread_mutexattr_setprotocol
Mutex attribute operations.
.It Fn pthread_mutexattr_gettype
Mutex attribute operations.
.It Fn pthread_mutexattr_settype
Mutex attribute operations.
.El
.Ss Non Portable Extensions
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_set_name_np()" -compact
.It Fn pthread_main_np
Identify the main thread.
.It Fn pthread_set_name_np
Set the name of a thread.
.It Fn pthread_stackseg_np
Return stack size and location.
.It Fn pthread_yield
Yield control of the current thread.
.El
.Ss Per-Thread Context Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_getspecific()" -compact
.It Fn pthread_key_create
Thread-specific data key creation.
.It Fn pthread_key_delete
Delete a thread-specific data key.
.It Fn pthread_getspecific
Get a thread-specific data value.
.It Fn pthread_setspecific
Set a thread-specific data value.
.El
.Ss Read/Write Lock Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_rwlockattr_getpshared()" -compact
.It Fn pthread_rwlock_init
Initialise a read/write lock.
.It Fn pthread_rwlock_destroy
Destroy a read/write lock.
.It Fn pthread_rwlock_rdlock
Acquire a read/write lock for reading.
.It Fn pthread_rwlock_timedrdlock
Attempt to acquire a read/write lock for reading before a specific
point in time.
.It Fn pthread_rwlock_tryrdlock
Attempt to acquire a read/write lock for reading without blocking.
.It Fn pthread_rwlock_wrlock
Acquire a read/write lock for writing.
.It Fn pthread_rwlock_timedwrlock
Attempt to acquire a read/write lock for writing before a specific
point in time.
.It Fn pthread_rwlock_trywrlock
Attempt to acquire a read/write lock for writing without blocking.
.It Fn pthread_rwlock_unlock
Release a read/write lock.
.It Fn pthread_rwlockattr_init
Initialise a read/write lock.
.It Fn pthread_rwlockattr_destroy
Destroy a read/write lock.
.It Fn pthread_rwlockattr_getpshared
Get the process shared attribute.
.It Fn pthread_rwlockattr_setpshared
Set the process shared attribute.
.El
.Ss Spinlock Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_spin_trylock()" -compact
.It Fn pthread_spin_init
Initialize a spinlock object.
.It Fn pthread_spin_destroy
Destroy a spinlock object.
.It Fn pthread_spin_lock
Lock a spinlock object.
.It Fn pthread_spin_trylock
Attempt to lock a spinlock without blocking.
.It Fn pthread_spin_unlock
Unlock a spinlock object.
.El
.Ss Thread Routines
The functions available are as follows:
.Pp
.Bl -tag -width "pthread_getconcurrency()" -compact
.It Fn pthread_create
Create a new thread.
.It Fn pthread_cancel
Cancel execution of a thread.
.It Fn pthread_detach
Detach a thread.
.It Fn pthread_equal
Compare thread IDs.
.It Fn pthread_exit
Terminate the calling thread.
.It Fn pthread_getconcurrency
Get level of concurrency.
.It Fn pthread_setconcurrency
Set level of concurrency.
.It Fn pthread_join
Wait for thread termination.
.It Fn pthread_kill
Send a signal to a specific thread.
.It Fn pthread_once
Dynamic package initialisation.
.It Fn pthread_self
Get the calling thread's ID.
.It Fn pthread_setcancelstate
Set cancelability state.
.It Fn pthread_setcanceltype
Set cancelability state.
.It Fn pthread_testcancel
Set cancelability state.
.It Fn pthread_sigmask
Examine/change a thread's signal mask.
.It Fn pthread_getcpuclockid
Get a CPU time clock for a thread.
.El
.Ss Thread stacks
Each thread has a different stack, whether it be provided by a
user attribute, or provided automatically by the system.
If a thread overflows its stack, unpredictable results may occur.
System-allocated stacks (including that of the initial thread)
are typically allocated in such a way that a
.Dv SIGSEGV
signal is delivered to the process when a stack overflows.
.Pp
Signals handlers are normally run on the stack of the currently executing
thread.
Hence, if you want to handle the
.Dv SIGSEGV
signal from stack overflow for a thread, you should use
.Xr sigaltstack 2
in that thread.
.Ss Thread safety
The following functions are not thread-safe:
.Bd -filled
asctime(),
basename(),
catgets(),
crypt(),
ctime(),
dbm_clearerr(),
dbm_close(),
dbm_delete(),
dbm_error(),
dbm_fetch(),
dbm_firstkey(),
dbm_nextkey(),
dbm_open(),
dbm_store(),
dirname(),
dlerror(),
drand48(),
ecvt(),
encrypt(),
endgrent(),
endpwent(),
fcvt(),
ftw(),
gcvt(),
getc_unlocked(),
getchar_unlocked(),
.\" getdate(),
getenv(),
getgrent(),
getgrgid(),
getgrnam(),
gethostbyaddr(),
gethostbyname(),
gethostent(),
getlogin(),
getnetbyaddr(),
getnetbyname(),
getnetent(),
getopt(),
getprotobyname(),
getprotobynumber(),
getprotoent(),
getpwent(),
getpwnam(),
getpwuid(),
getservbyname(),
getservbyport(),
getservent(),
gmtime(),
hcreate(),
hdestroy(),
hsearch(),
inet_ntoa(),
l64a(),
lgamma(),
lgammaf(),
lgammal(),
localeconv(),
localtime(),
lrand48(),
mrand48(),
nftw(),
nl_langinfo(),
putc_unlocked(),
putchar_unlocked(),
putenv(),
rand(),
readdir(),
setenv(),
setgrent(),
setkey(),
setpwent(),
strerror(),
strsignal(),
strtok(),
ttyname(),
unsetenv(),
wcstombs(),
wctomb()
.Ed
.Pp
The
.Fn ctermid
and
.Fn tmpnam
functions are not thread-safe when passed a
.Dv NULL
argument.
The
.Fn wcrtomb ,
.Fn wcsrtombs ,
and
.Fn wcsnrtombs
functions are not thread-safe when passed a
.Dv NULL
.Fa ps
argument.
.Sh ENVIRONMENT
.Bl -tag -width "RTHREAD_DEBUG"
.It Ev RTHREAD_DEBUG
Enables debugging output when set to a positive number,
with larger numbers generating more verbose output.
.El
.Sh SEE ALSO
.Xr intro 3 ,
.Xr pthread_atfork 3 ,
.Xr pthread_attr_init 3 ,
.Xr pthread_attr_setdetachstate 3 ,
.Xr pthread_attr_setguardsize 3 ,
.Xr pthread_attr_setstack 3 ,
.Xr pthread_attr_setstackaddr 3 ,
.Xr pthread_attr_setstacksize 3 ,
.Xr pthread_barrier_init 3 ,
.Xr pthread_barrier_wait 3 ,
.Xr pthread_barrierattr_getpshared 3 ,
.Xr pthread_barrierattr_init 3 ,
.Xr pthread_cancel 3 ,
.Xr pthread_cleanup_pop 3 ,
.Xr pthread_cleanup_push 3 ,
.Xr pthread_cond_broadcast 3 ,
.Xr pthread_cond_destroy 3 ,
.Xr pthread_cond_init 3 ,
.Xr pthread_cond_signal 3 ,
.Xr pthread_cond_timedwait 3 ,
.Xr pthread_cond_wait 3 ,
.Xr pthread_condattr_init 3 ,
.Xr pthread_create 3 ,
.Xr pthread_detach 3 ,
.Xr pthread_equal 3 ,
.Xr pthread_exit 3 ,
.Xr pthread_getcpuclockid 3 ,
.Xr pthread_getspecific 3 ,
.Xr pthread_join 3 ,
.Xr pthread_key_create 3 ,
.Xr pthread_key_delete 3 ,
.Xr pthread_kill 3 ,
.Xr pthread_main_np 3 ,
.Xr pthread_mutex_destroy 3 ,
.Xr pthread_mutex_init 3 ,
.Xr pthread_mutex_lock 3 ,
.Xr pthread_mutex_unlock 3 ,
.Xr pthread_mutexattr 3 ,
.Xr pthread_once 3 ,
.Xr pthread_rwlock_destroy 3 ,
.Xr pthread_rwlock_init 3 ,
.Xr pthread_rwlock_rdlock 3 ,
.Xr pthread_rwlock_unlock 3 ,
.Xr pthread_rwlock_wrlock 3 ,
.Xr pthread_rwlockattr_destroy 3 ,
.Xr pthread_rwlockattr_getpshared 3 ,
.Xr pthread_rwlockattr_init 3 ,
.Xr pthread_rwlockattr_setpshared 3 ,
.Xr pthread_schedparam 3 ,
.Xr pthread_self 3 ,
.Xr pthread_set_name_np 3 ,
.Xr pthread_setspecific 3 ,
.Xr pthread_sigmask 3 ,
.Xr pthread_spin_init 3 ,
.Xr pthread_spin_lock 3 ,
.Xr pthread_spin_unlock 3 ,
.Xr pthread_stackseg_np 3 ,
.Xr pthread_testcancel 3 ,
.Xr pthread_yield 3
.Sh STANDARDS
The thread library provides functions that
conform to
.St -p1003.1-96
and various later versions of
.Pq Dq Tn POSIX .
Please consult the manpages for the individual functions for details.
.Sh HISTORY
This 1-to-1 implementation of the
.Nm
API initially appeared in
.Ox 3.9
under the name
.Dq librthread
as an alternative to the pure-userspace (N-to-1) implementation.
In
.Ox 5.2
it became the default implementation and was renamed to
.Dq libpthread .
.Sh AUTHORS
.An -nosplit
.An Ted Unangst Aq Mt tedu@openbsd.org ,
.An Kurt Miller Aq Mt kurt@openbsd.org ,
.An Marco S Hyman Aq Mt marc@openbsd.org ,
.An Otto Moerbeek Aq Mt otto@openbsd.org ,
and
.An Philip Guenther Aq Mt guenther@openbsd.org .
